Safety systems for power tools are disclosed in International Application Number PCT/US00/26812, filed Sep. 29, 2000, and published as International Publication Number WO 01/26064 A2 on Apr. 12, 2001, the disclosure of which is hereby incorporated by reference. That application claims priority to a number of priority documents, including U.S. Provisional Patent Application Ser. No. 60/157,340, filed Oct. 1, 1999. The safety systems disclosed in that application include a detection system adapted to detect a dangerous condition between a person and a working portion of a machine, such as accidental contact with the working portion, and a reaction system associated with the detection system to cause a predetermined action to take place relative to the working portion upon detection of the dangerous condition by the detection system. The reaction system may be a retraction system to retract the working portion. Machines equipped with safety systems are also disclosed.
Retraction systems for use in power equipment are also disclosed in U.S. Pat. No. 7,509,899, filed Aug. 13, 2001 and issued Mar. 31, 2009, and that patent is also hereby incorporated by reference. The retraction systems disclosed in that patent are configured to retract a cutting tool at least partially away from a cutting region upon detection of a dangerous condition by a detection system.
Power tool safety mechanisms are also disclosed in International Application Number PCT/US02/21790, filed Jul. 11, 2002, and published as International Publication Number WO 03/006213 A2 on Jan. 23, 2003. That application claims priority to a number of priority documents, including U.S. Provisional Patent Application Ser. No. 60/304,614, filed Jul. 11, 2001. That application discloses a sensing mechanism for detecting user contact with an active portion of a power tool, and a system to rapidly displace the active portion away from a user extremity, or alternatively, to rapidly urge an extremity of the user away from the active portion of the power tool.
Other retraction systems for power tools are disclosed in U.S. Pat. No. 6,922,153, filed May 13, 2003 and issuing on Jul. 26, 2005. That patent discloses using a pyrotechnic and propellant to pivot a saw blade down or using a flywheel to do so.
A pyrotechnic drop mechanism for power tools is disclosed in U.S. Pat. No. 7,628,101, filed Oct. 30, 2006 and issued Dec. 8, 2009. That patent discloses using a pyrotechnic to move a piston and retract a saw blade.
At least as early as Mar. 19, 2010, a German company called Altendorf posted on the Internet an article describing a hand detection sensor for use on wood processing machinery. That system uses a near-infrared sensor that purportedly can tell the difference between human skin and wood and other materials. Upon detection of human skin, a deflector or shutter stops the user's hand from reaching the saw blade.
German patent document DE 196 09 771 A1, with a publication date of Jun. 4, 1998, describes a safety system for a circular saw bench in which a Theremin oscillator purportedly detects the proximity of a hand to a blade and a pneumatic cylinder then retracts the blade.